Our goal is to gain an understanding of myosin expression in the conduction system of the human heart. Preliminary studies demonstrate that the myosin heavy chain isolated from the human SA node is distinctly different from the alpha and beta heavy chains of the atria and ventricles. Peptide mapping of affinity purified myosin from different components of the conduction system will be conducted to determine if common or multiple myosin heavy chains are produced in the conduction system. Monoclonal antibodies will be produced against affinity purified myosin isolated from the human conduction system to generate specific probes to study. The specificities of these antiboties for the conduction system will be documented by radioimmunoassay and immunoblotting analysis of myosin isolated of myosin expression within individual components of the conduction system will be analyzed by immunofluorescence microscopy. After the specificities of these antibodies have been determined for the adult conduction system, the same probes will be used as specific markers of conduction system myocytes to examine the development of these specialized muscle cells. In these studies, immunofluorescence microscopy and radioimmunoassay with specific antibodies will be employed to study the elaboration and maintenance of specific conduction system components during cardiac myogenesis. It is hoped that these studies will aid in understanding the cellular mechanisms of conduction system myogenesis and lay the groundwork for the future examination of the conduction system in abnormal cardiac development and in the diseased adult heart.